U.S. application Ser. No. 07/599,751, filed Oct. 19, 1990 by me under the title FLUORINE-FREE PHOSPHATE GLASSES, now U.S. Pat. No. 5021,366, is directed to the preparation of chemically durable, weather resistant, essentially fluorine-free glass compositions with annealing points within the range of about 300.degree.-340.degree. C., thereby enabling them to be molded into lenses at temperatures of about 360.degree.-400.degree. C., and with refractive indices of about 1.605 and linear coefficients of thermal expansion (25.degree.-300.degree. C.) between 145-170.times.10.sup.-7 /.degree.C. Those glasses were designed to replace the alkali metal fluoroaluminophosphate glasses disclosed in U.S. Pat. No. 4,362,819 (Olszewski et al.) marketed by Corning Incorporated, Corning, New York for pressing optically finished lenses as described in U.S. Pat. No. 4,481,023 (Marechal et al.) As was explained in that application, fluorine in the glasses attacked the surfaces of the molds during pressing of the lenses, and volatilization thereof during melting of the glass batch gave rise to environmental hazards. The glasses of U.S. Ser. No. 07/599,751 consisted essentially, expressed in terms of mole percent on the oxide basis, of:
______________________________________ Li.sub.2 O 5-10 P.sub.2 O.sub.5 30-36 Na.sub.2 O 5-15 Al.sub.2 O.sub.3 0-5 K.sub.2 O 0-6 CeO.sub.2 0-2 Li.sub.2 O + Na.sub.2 O + K.sub.2 O 15-25 SnO 0-20 ZnO 10-33 PbO 0-20 CaO 0-20 Sb.sub.2 O.sub.3 0-12 SrO 0-20 Bi.sub.2 O.sub.3 0-6 BaO 0-20 SnO + PbO + Sb.sub.2 O.sub.3 + 0-20 Bi.sub.2 O.sub.3 ______________________________________
The primary objective of the instant invention was to devise fluorine-free glass compositions demonstrating chemical and physical properties similar to those exhibited by the glasses of U.S. Ser. No. 07/599,751, but wherein refractive indices ranging from at least 1.65 to values in excess of 1.8 can be achieved. In like manner to the definition set out in U.S. Ser. No. 07/599,751, the expression essentially fluorine-free indicates that no material containing substantial concentrations of fluorine is intentionally included in the glass.